Control device for an occupant safety device of motor vehicles

ABSTRACT

In a control device for a passenger safety apparatus, the safety apparatus is triggered by a sensor arrangement which responds to a longitudinal and/or transverse acceleration of the motor vehicle. It is also independently triggerable by an additional state-of-motion or moving-condition sensor which is configured to recognize a near weightless state of the vehicle. The safety apparatus is triggered even in an extremely critical state of motion in which the vehicle moves in a manner similar to free fall.

BACKGROUND OF THE INVENTION

The present invention relates to a control device for a motor vehicleoccupant safety apparatus and, more responsive to longitudinal and/ortransverse acceleration.

Control devices for the triggering of air bags, roll-over bars and thelike are generally known. They respond when the measured accelerationexceeds the limit which is customary during a noncritical operation ofthe motor vehicle. The values involved may be absolute values or theduration of the measured acceleration as well as combinations of valuesand duration of this acceleration.

However, in the case of these known control devices, the safety deviceis, as a rule, not triggered when the motor vehicle is in a particularlycritical condition. This critical condition will occur when the motorvehicle loses contact with the road by, for example, crashing downward.

The present invention is based on an object of providing a controldevice which triggers the occupant safety device particularly when themotor vehicle is in a particularly critical situation.

The invention achieves this object by providing an additionalmoving-condition sensor to trigger the safety apparatus independently ofthe acceleration sensor when the motor vehicle approaches a weightlesscondition.

In the case of weightlessness, such as arises from free fall theacceleration values in the motor vehicle are relatively low.Nevertheless, the safety device must already be triggered during thefree fall since extremely high acceleration values frequent occur at theend of the weightless condition (impact). The present invention that thesafety device to become operative already during the weightlesscondition in order to thus provide a sufficient protection for thevehicle occupants at the end of the weightlessness condition.

Since a condition of the motor vehicle which approaches weightlessnessoccasionally occurs during the normal driving operation, a furtherfeature of the present invention differentiates between such "normal"and "critical" situations. In order to avoid an unnecessary triggeringof the safety device in situations of this type which occur, forexample, when driving over a hilltop, the duration of the criticalcondition is determined by a time function element. When this durationis short, that is, the critical condition is very brief with respect totime, the occupant safety device is not triggered. The circuit devicesrequired for achieving this feature of the invention include connectinga time-function element behind the moving-condition sensor.

During the condition of weightlessness, a distance measuring sensordetermines a distance from the ground which is clearly above the normalvalue. During the weightless condition, the sensor furnishes a valueclose to zero. Finally, the rebound of one or several of the vehiclewheels, when it is equal to the maximally possible value, is also a goodindication of the condition of weightlessness.

Although a safety device for a roll-over bar of a motor vehicle is knownfrom German Patent Document DE-PS 35 45 874 which is controlled by arebound sensor, in contrast to the present invention, the free fallcondition is not taken into account because the signal of the wheelrebound sensor will only have an effect when a tilt switch responds atthe same time which is actuated when a certain tilt is exceeded.However, during the weightless condition, there is frequently nofunctional connection with the tilt of the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing figure which is a schematic circuit for a controldevice for actuating an occupant safety system; and

FIG. 2 is a schematic circuit for another embodiment of a control devicefor actuating an occupant safety system.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS

The drawing shows a control device in accordance with the presentinvention for an occupant safety device which can be triggered by asensor device 1 and can, independently of it, be triggered by amoving-condition sensor 2. This is alternative triggering is symbolizedby an OR-function element.

The safety device is, for example, a known air bag or a roll-over bar(not shown) of a motor vehicle. The sensor device 1 may, for example, beconstructed as described in German Patent Application with the officialGerman File Number P 38 15 938.4 or may consist of one or several leveltubes. However, it is also possible to use any other known construction,and to determine the transversal acceleration or the rotationalcondition by movable mass bodies.

The moving-condition sensor 2 may, for example, respond to the verticalacceleration of the motor vehicle and, together with the sensor device1, may be integrated in a common housing 3. In the simplest case, thesensor 2 is a scale 4 by which the weight of the mass body 5 isdetermined.

During normal driving conditions, the scale 4 indicates a value whichfluctuates around the value of the actual weight. The fluctuations arecaused by temporary, relatively slight vertical accelerations which themotor vehicle experiences during the driving operation.

When the motor vehicle loses the contact with the ground, a movingcondition occurs which is at least similar to that of weightlessness.The scale 4 now furnishes a value which, in the ideal case, that is, inthe undisturbed free fall, is equal to zero or is around this valuewithin a small value range.

The control device therefore recognizes the condition of weightlessness.When this conditions lasts for a specific time period, for example, 100msecs, the control device triggers the air bag or the roll-over bar andrenders it operative. The given time period is determined by a timefunction element 6 through which the output signal of the scale 4 isguided.

The triggering of the safety device by the moving-condition sensor 2takes place independently of the possible triggering by the accelerationsensor 1 and therefore also when the latter determines no critical valueof the measured acceleration. Thus, it is ensured that under allpossible moving conditions of the motor vehicle, the safety device istimely triggered and therefore carries out its function reliably.

Instead of the illustrated scale-like driving-condition sensor 2, adistance sensor, (not shown), which determines the distance of the motorvehicle from the road surface, or a wheel rebound sensor, and respondsin the case of a maximally rebound vehicle wheel, may also be used forrecognizing that the vehicle has lost contact with the road or has stillonly a very slight contact with the road which approaches the conditionof the free fall.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample, and is not to be taken by way of limitation. The spirit andscope of the present invention are to be limited only by the terms ofthe appended claims.

I claim:
 1. A control device for an occupant safety device of motorvehicles, comprising a sensor device responding to at least one oflongitudinal and transversal acceleration for triggering the safetydevice, and an additional moving-condition sensor which solely andindependently of the sensor device triggers the safety device only whenthe motor vehicle is in a substantially weightless condition for aspecific time period.
 2. The control device according to claim 1,wherein a time function element is connected behind the moving-conditionsensor, and the safety device is configured to be triggered when thevehicle is in the substantially weightless condition for longer than aswitching time of the time function element.
 3. The control deviceaccording to claim 1, wherein the moving-condition sensor is a distancesensor which determines a distance of the motor vehicle from a roadsurface.
 4. A control device according to claim 1, wherein themoving-condition sensor responds to vertical acceleration.
 5. Thecontrol device according to claim 1, wherein the moving-condition sensoris a wheel rebound sensor.
 6. The control device according to claim 2,wherein the moving-condition sensor is a distance sensor whichdetermines a distance of the motor vehicle from a road surface.
 7. Acontrol device according to claim 2, wherein the moving-condition sensorresponds to vertical acceleration.
 8. The control device according toclaim 2, wherein the moving condition sensor is a wheel rebound sensor.